Monday, February 16, 2015

Mystery of the Month - February 2015

Winter: Humans Survive & Bugs Do Too

"Monarch-butterflies-pacific-grove" by Agunther - Own work. Licensed
under CC BY 3.0 via Wikimedia Commons -
Link to image HERE.

By Zola Pineles

Winter is coming. Winter is…here! For humans, heat and comfort in the cold months can be relatively easy to procure thanks to amenities such as shelter, warm layers, our wits, and central heating. For insects, the winter means employing a number of different strategies to ensure survival.

Depending on the insect, diapause, freeze tolerance/avoidance, migration, and life cycle variations are methods that keep bugs crucial to Minnesota’s ecosystem alive for another season.


Diapause is a state of suspended metabolic activity brought upon by external stimuli. In other words, when the days begin to shorten, and before the temperatures drop severely, insects increase their resistance to environmental extremes by storing additional energy reserves for the long winter. Similar to higher animals that undergo hibernation, insects will find space underground, beneath debris, in galls (bulbous outgrowth on some plant tissue), or in cocoons.

While in their respective shelters, insects dramatically reduce their activity to prolong their stored energy. For some insects, diapause occurs only if certain environmental factors cause a hormone in the brain to halt production and temporarily pause at the embryonic, larval, pupal, or adult stages of life.

When environmental conditions once again become favorable, the same hormone production picks up and the insect goes on its merry way to the next life stage.


Here are examples of some insects that undergo diapause: 
  • Southwestern Corn Borer (late larval diapause)
  • Silkworm (embryonic diapause)
  • Gypsy month (late embryonic diapause)

Freeze Tolerance

Have you ever seen a science fiction movie where a character will cryogenically freeze or preserve themselves in low temperatures to be defrosted in exactly the same state years into the future? That’s kind of what some insects do to survive the winter temperatures.
Many species of insects have developed a tolerance to ice crystallization within the cells of the body to allow preservation through the cold winter months. Cryoprotectants, primarily glycerol, are small molecules within the fluids of the insects’ body that bind together and drop the internal freezing point of the insect. Freeze tolerance varies widely and can allow species such as the Alaskan beetle to survive at temperatures as low as -124°F.

Here are examples of some insects that are freeze tolerant.
  • Wooly bear
  • Flightless midge
  • Alpine cockroach
  • queen bumblebees

 Freeze Avoidance

"GoldenrodGallFlyLarva" by SriMesh - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons -

While some insects embrace the cold and turn their bodies to ice, others avoid freezing at all costs. Supercooling is one method that some insect species use to prevent from freezing internally. Supercooling can only occur when the fluids within the insect are so pure that ice crystallization cannot occur – ice formation is dependent on the presence of a particle on which to attach – therefore the fluids do not turn to ice and injury is prevented during the cold winter months. This allows the bodies of some insects to remain unfrozen in temperatures as low as -76°F.

Here are examples of some insects that are freeze avoidant:
  • Gall Moth
  • Pine beetle
  • Emerald Ash Borer
  • Aphids
  • Ticks


Monarch butterflies, like these flocking
to a blazing star bloom at our office in August,
migrate to warmer weather in the winter.
While some insects choose the hardy route and stick out the winter in subzero conditions, others choose to go someplace warmer. Migration is a technique that is used by a number of species, most notably monarch butterflies. During the summer months, adult monarchs mate and lay eggs which become the next generation. The last generation halts reproductive capabilities in order to make the southward journey. When October arrives, Monarchs east of the Rocky Mountains fly south to mountain highlands near Mexico City. Monarchs west of the Rocky Mountains fly south to Santa Barbara, California. When the cold winter months are over, the last generation of monarchs that flew down south makes the return journey north.

Here are examples of insects that migrate in the winter:
  • Darner dragonfly
  • Monarch butterfly
  • Desert locust

In the End....

Though just a few overwintering techniques were listed, it is clear that insects have become highly evolved to withstand the same, if not worse conditions than we do. So next time you are feeling cold and you go to turn up the thermostat, think about the little things outside and be thankful.

1 comment:

  1. Western Monarch butterflies overwinter at a number of sites in California, not just Santa Barbera, according to this 1997 document: